Each of Japanese Laid-Open Patent Publications Nos. 2000-198047 and 2001-038502 discloses an NC lathe in which tools are mounted on a turret while a work is held by a chuck. The chuck is rotated about a drive shaft. The turret or the chuck is moved by an NC device in a direction of X-axis and a direction of Z-axis to machine the work with the tool.
In addition, the turret has a plurality of mounting positions. The turret is rotated about a support shaft, the mounting positions being spaced from each other equiangularly about the support shaft. Tools are mounted at the mounting positions. A motor is connected to the turret, the turret being rotated by the motor, so that the tool can be exchanged for another by the turret. In the NC lathe, under the recent sophistication of machining, it is required to increase the number of tools to be exchanged.
By the way, Japanese Patent Publication No. 3571605 discloses an index apparatus of push bar type for a machining center. Speaking just for reference with the knowledge of no direct relationship with the NC lathe, the machining center includes an NC device by which a spindle or a main table is moved to machine a work with a tool. In addition, the spindle or the main table is moved by the NC device independently of machining to make a push bar moved longitudinally thereof, an index table being rotated in response to the push bar to index the work.
It is therefore an object of the invention to provide an NC lathe which can increase the number of tools to be exchanged.